class Solution {
    vector<int> ret;
    vector<int> index;
    int tmpNums[100001];
    int tmpIndex[100001];
public:
    vector<int> countSmaller(vector<int>& nums)
    {
        int n = nums.size();
        ret.resize(n);
        index.resize(n);

        for (int i = 0; i < n; i++)
        {
            index[i] = i;
        }

        mergeSort(nums, 0, n - 1);
        return ret;
    }

    void mergeSort(vector<int>& nums, int left, int right)
    {
        if (left >= right) return;

        int mid = (left + right) >> 1;
        mergeSort(nums, left, mid);
        mergeSort(nums, mid + 1, right);

        int i = 0, cur1 = left, cur2 = mid + 1;
        while (cur1 <= mid && cur2 <= right)
        {
            if (nums[cur1] <= nums[cur2])
            {
                tmpNums[i] = nums[cur2];
                tmpIndex[i++] = index[cur2++];
            }
            else
            {
                ret[index[cur1]] += right - cur2 + 1;
                tmpNums[i] = nums[cur1];
                tmpIndex[i++] = index[cur1++];
            }
        }

        while (cur1 <= mid)
        {
            tmpNums[i] = nums[cur1];
            tmpIndex[i++] = index[cur1++];
        }
        while (cur2 <= right)
        {
            tmpNums[i] = nums[cur2];
            tmpIndex[i++] = index[cur2++];
        }

        for (int i = left; i <= right; i++)
        {
            nums[i] = tmpNums[i - left];
            index[i] = tmpIndex[i - left];
        }
    }
};